Development of an integrated thermal and enzymatic hydrolysis for lignocellulosic biomass in fixed-bed reactors

Abstract

The limitations of the current biorefinery process utilizing stirred-tank reactors for the enzymatic step include poor mixing in the case of high biomass loadings, additional steps for the product separation, and a long reaction time. In this study the hydrothermal pretreatment and the enzymatic hydrolysis of the lignocellulosic biomass were combined in one fixed-bed reactor. The influence of the shear forces during recirculation and enzyme stability at elevated temperatures were investigated. It has been shown that the shear forces resulting from pumping have a negligible effect on enzyme activity. However, large pressure drops reduce the enzyme activity significantly. Furthermore, the enzyme stability was significantly increased at elevated temperatures (60°C) by applying static pressures up to 200 bar (56% residual activity at 60°C after 24 h). This is beneficial for the process as a higher temperature accelerates the reaction. Further improvement of the overall process efficiency was achieved by increasing the solid-to-water ratio and circulation of the enzyme solution. At a biomass content of 7%, a glucose concentration of 61 g l-1 and a yield of 85% was achieved. The integrated process was first done on a laboratory scale (50 ml). At 100 bar, 60°C and 10% biomass loading an increased initial reaction rate was observed. However, this effect was followed by the stagnation of the glucose yield as one of the enzymes, Novozyme 188, showed no remarkable stabilization with pressure. Nevertheless, an overall glucose yield of 40% was achieved after 5.5 h, compared to 14 h under normal pressure and 50°C.

High Pressure Processes in Biorefineries

“…In our group the realization of the enzymatic hydrolysis in the fixed bed reactor allowing to increase the solid to liquid ratio was studied [24]. It was shown, that the shear forces appearing in the flow-through system have a relatively small influence on the enzymatic activity.…”

“…It was shown, that the shear forces appearing in the flow-through system have a relatively small influence on the enzymatic activity. By contrast, enzyme deactivation in a valve showed remarkable deactivation during expansion of the enzyme solution with increasing pressure and should therefore be prevented [24]. Habulin has also observed changes in biocatalyst activity due to pressurization/depressurization steps which were studied in a high-pressure batch stirred tank reactor [25].…”

“…Several authors reported a positive influence of high pressure on the thermal stability of enzymes [17]. Kirsch et al showed that several cellulases and xylanases are stabilized at elevated temperatures, if pressure in the range of 100 -300 bar is applied [24]. Consequently, enzymatic hydrolysis in a fixed bed reactor can be carried out at elevated pressure and temperature.…”

Determination of the diffusion of monovalent cations into wood under isothermal conditions based on LiCl impregnation of Norway spruce

“…It is believed that biorefinery will play a significant role in forest clusters worldwide ( N ä yh ä and Pesonen 2012 ). There are huge research efforts in the field of biorefinery aiming at the production of value-added products (Ragauskas et al 2006 ;Dautzenberg et al 2011 ;G ü tsch and Sixta 2011 ;H ö rhammer et al 2011 ;Kirsch et al 2011 ;L ó pez et al 2011;Martin -Sampedro et al 2011 ;Sch ü tt et al 2011 ;Testova et al 2011 ). For example, the extraction of a portion of hemicelluloses from wood before pulping -by acid hydrolysis, autohydrolysis, steam explosion, or alkali extraction -seems to be promising in this context.…”

Extracting value-added products before pulping: Hemicellulosic ethanol from Eucalyptus globulus wood

“…When performed under suitable conditions, autohydrolysis leads to xylan breakdown (yielding soluble saccharides), whereas the remaining solid can still be suitable for pulping (Vila et al 2011 ). When autohydrolysis is performed under harsh conditions, solids can be subjected to aqueous processing, which yields cellulose-containing solids suitable as substrates for enzymatic hydrolysis; therefore, the production of glucose solutions suitable as media for ethanol fermentation is possible (Weil et al 1997 ;Kirsch et al 2011 ). Operation in a percolation reaction at 200 -230 ° C with residence times of up to 15 min enabled the recovery of more than 90 % of hemicelluloses as soluble saccharides, with similar behavior for different types of lignocellulosic substrates (including both woody and non-woody materials) (Mok and Antal 1992 ).…”